This proposal outlines a basic research plan for studying the mechanism of regulation of muscle contraction as mediated by calcium-binding proteins. In particular, the structural and functional relationships of parvalbumin and troponin C will be investigated. The amino acid sequences of both parvalbumin and troponin C have been determined, and comparison of these structures have revealed a high degree of homology, Thus, the high-resolution structure currently available for parvalbumin (Three-dimensional structure to 1.8 A resolution) provides an excellent basis for further defining the functional and regulatory properties of both proteins in terms of their detailed molecular features. The three-dimensional and primary structures will be used as a rational basis for applying chemical modification, protein-fragmentation and physical-chemical techniques in order to identify specific amino acid residues and larger elements of structure which are essential for biological function. The information which is available relating to the regulation of muscle contractile proteins will be extended to study the regulation of non-muscle contractile proteins. In particular, the role of contractile proteins in secretion of catecholamines by the adrenal medulla will be examined. The actomyosin-like proteins in the adrenal medulla will be purified and their regulatory properties investigated. The amino-acid sequence of the adrenal medulla high affinity calcium-binding protein will be determined and its relationship to troponin C will be accessed.